Hydraulic buffer to protect buildings against earthquakes

ABSTRACT

A hydraulic buffer, filled with a compound having the behaviour of a liquid to a certain extent, mounted beneath the foundation of buildings or other structures in order to sustain the structures during earthquakes. The buffer is made from reinforced flexible material and consists of two parallel circular plates (1,2), on the circumference connected to each other by a torus (5), in such a way that the torus and the drum-like space between the circular plates communicate freely, while the axis of the torus is upright, in order to permit the buffer to accommodate relative transverse movement between the circular plates.

BACKGROUND OF THE INVENTION

The invention relates to a hydraulic buffer, filled with a compound thatbehaves like a liquid to a certain extent, mounted beneath thefoundations of buildings and other structures in order to absorb theshocks of severe earthquakes.

SUMMARY OF THE INVENTION

The buffer according to the invention has an envelope made of flexiblematerial, preferably rubber and preferably reinforced by any fabric, andformed with two parallel circular plate portions, separated by a layerof a compound with a liquid behaviour. The circular portions areconnected to each other along their circumferences by a hollow torus, insuch a way that the interior of the torus and the space between thecircular plate portions communicate freely when the torus is mountedwith its axis upright. The circular plate portions of flexible materialare supported or backed by discs made from any rigid material like steelor aluminum, or by a square concrete plate. When the torus rests on asmooth surface, the lower rigid disc can be omitted in most cases.Furthermore, the envelope is provided with two access nipples, one forintroducing the liquid-like compound and the other for venting purposesduring filling of the buffer by a special filling device. Each nipplehas a shutoff valve (not shown).

The number of buffers, the allowable load, and the hydrostatic pressureinside the buffer depend on the weight of the building underconsideration, the construction of the foundation, and the energyabsorption capability of the ground beneath the foundation.

The width of the torus should be selected such that the allowableamplitude of ground displacement shall be in accordance with localearthquake design specifications. Although the force shall be assumed toact in any horizontal direction, in most cases horizontal and verticalforces are acting simultaneously. For that reason the design shall alsomeet the requirement for fluctuating vertical load.

Since in several regulations for earthquake sensitive regions themaximum acting ground displacement is assumed at ninety centimeters, thetorus should have at least the same width. In some cases it will beadvisable that the buffers for a building or other structure behydraulically connected to equalize the hydrostatic pressure duringand/or after earthquakes. This is especially an advantage when permanentdisplacements remain.

It is an object of the invention to provide a safety device to protectbuildings and other structures from damage and collapse duringearthquakes that often result in disasters at the cost of many victimsand much money.

The advantage of the invention when it is compared with existing safetydevices, serving the same purpose and already known, are the uniformload, the large range of allowable ground displacement, the extremelylow forces in the flexible parts of the buffer, resulting in a longrated life, a low resistance of the torus against the acting grounddisplacements during earthquakes, the self level adjusting capability,and the simplicity of the design.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will be explained, by way of example,with reference to the accompanying drawing, in which

FIG. 1 is an elevation view, in cross section, of the hydraulic bufferassembly,

FIG. 2 represents a detail, at an enlarged scale, of a portion of thehydraulic buffer, and

FIG. 3 is a detail of one of the access nipples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the figures, the preferred embodiment of the hydraulicbuffer includes an impervious envelope 13 made of flexible material. Thematerial is preferably rubber or rubber-like. Desirably, the torus isreinforced by metal wire or bars, radially inserted in the flexiblematerial, in such a way that the final flexibility is not affected bythe reinforcement. The envelope includes a first circular upper plateportion 1 and a second circular base plate portion 2 spaced from andcoaxial with the first circular portion. A hollow torus 5 coaxiallysurrounds and is connected to the first and second circular plateportions to form a continuous surface.

When the buffer is loaded under normal conditions, the upper circularplate portion 1 is parallel to the lower circular plate portion 2, whilethe flexible material of the upper circular plate portion 1 is coveredand supported or backed by the metal disc 3, to the circumference ofwhich is welded a toroidal tube 4, intended to achieve a gradualtransition from the circular portion 1 into the torus 5 for avoidingdamage to the neck of the torus.

The liquid-like compound 6, preferably oil or fresh water or a compoundof several materials behaving as a liquid, must be pumped into thebuffer through the access nipple 7, and the trapped air can escapethrough the nipple 8. During pumping of the liquid-like compound 6 intothe buffer, the torus 5 becomes full-shaped first. As more liquid-likecompound 6 is pumped into the buffer, the upper circular plate portion 1together with the metal disc 3 become lifted, and consequently thefoundation support 9 also. The required quantity of liquid-like compounddepends on the distance between the circular plates 1 and 2 necessary toavoid direct contact during tilting when the earth at the spot is inmotion. In order to avoid damaging the lower circular plate portion 2,the ground 10 shall be smoothly finished by means of a layer of bitumen11, of rubber, or otherwise.

In some cases special cross beams 12 will be necessary to givesufficient support to the foundation in horizontal directions. Shockabsorption in vertical directions is also possible if the torus 5 ispartially filled with inert gas, which is to be considered when theenergy absorption capability of the ground should be insufficient.

Another advantage of the invention not mentioned yet is the very smalldistance needed between the bottom of the foundation and the ground,only enough to pass the diameter of the toroidal tube plus the thicknessof the circular plate portions, when the buffer is being installed inits final position. That means a minimum of excavation when the bufferis installed under existing buildings and other structures. In general,the thickness of the liquid layer between both circular plate portionsshall be such as to avoid direct contact of the plates when tilting,caused by local subsidence, PG,6 sometimes occurs during severeearthquakes.

During earthquakes the ground displacements affect the volume of thetorus; it becomes smaller. This is immediately compensated by enlargingthe distance between the circular plates. That produces a slight dampingof the tremors and also forces the building under consideration toreturn to its original position when the earthquakes have passed.Sometimes the above mentioned behaviour of the hydraulic buffer can be areason to fill the buffer partly with an inert gas. In that case thebuffer is also effective in vertical directions and the applied load dueto dead-load plus earthquake load, sometimes equal to one g, is moregradually absorbed by the buffer, especially by the torus. The bufferaccording to the invention is also applicable for shock absorption ingeneral.

Additional preferred features of the invention include a lid-like organ(not shown) to protect the buffer from damage caused by falling objects,reinforcement of the base plate portion of the buffer by metal wire orstrips or metal inserts. In addition, the buffer may include a knowndevice, such as a coil spring, to compensate for vertical grounddisplacements, in such a way that the compensating elements areconnected to the upper circular plate portion of the buffer according tothe invention. Further, a certain number of balls may be placed betweenthe upper and lower plate portions, in such a way that under normalconditions the upper plate portion does not have any point of contactwith the balls. The balls become effective only when the buffer envelopeis leaking, avoiding collapse of the supported part of the building.

I claim:
 1. A hydraulic buffer for absorbing large transversedisplacements between a supporting surface and a structure, the buffercomprising:an impervious envelope made of flexible material, theenvelope including a first circular upper plate portion, a secondcircular base plate portion spaced from and coaxial with the firstcircular plate portion, and a hollow torus having a wall coaxiallysurrounding and connecting the first and second circular plate portions,the wall of the torus and the first and second plate portions forming acontinuous surface, and the hollow interior of the torus communicatingfreely with the space between the first and second plate portions; aliquid-like material filling the space between the first and secondplate portions and at least partially filling the hollow torus; and arigid disc placed on the flexible material of the first circular upperplate portion to provide a bearing surface for the structure, the dischaving a rounded circumferential edge to provide a smooth transitionfrom the circumference of the upper plate portion to the connecting wallof the torus.
 2. A hydraulic buffer according to claim 1 wherein theliquid-like material is oil.
 3. A hydraulic buffer according to claim 1wherein the liquid-like material is pure water.